Electric hair removal apparatuses are frequently operated by means of integrated batteries, in particular rechargeable batteries. In this way it is possible to prevent the handling of the hair removal apparatuses being obstructed by cords. Because the storage capacity of the batteries is limited, it is desirable to make the most efficient possible use of the stored electric power. A large part of the electric power consumed on operating the hair removal apparatuses is not used directly for removing the hairs but is wasted, for example, through friction in the drive train of the hair removal apparatuses. This means that there is a considerable consumption of electric power during the operation of hair removal apparatuses even when no or only few hairs are being removed.
To keep the power consumption in limits and still achieve an adequate removal of hair, hair removal apparatuses are often designed for anticipated average operating conditions. This results however in the hair removal apparatuses causing vibrations and noises under no-load conditions, i.e., when no hairs are being removed, and displaying an inadequate function under full-load conditions, i.e., when very many hairs are being removed. This undesirable behavior can be counteracted by controlling the rotational frequency of the drive motor of the hair removal apparatus.
For example, from DE 42 01 027 A1 and U.S. Pat. No. 5,367,599 there is known an electric shaver that deduces whether a beard is thick or thin dependent on the load current of the motor. The motor is then controlled on the basis of the determined beard thickness. With a thin beard the motor is operated at a low rotational speed; with a thick beard it is operated at a high speed.
From EP 0 719 202 B 1 there is known a shaving apparatus with an electric motor whose speed is varied by a forward-coupled closed-loop control unit as a function of at least one physical variable. The physical variable is measurable by means of a detecting element that detects an audio signal for determining the hairs cut per unit of time, the elapsed shaving time, or a skin contact force.